While editing the column you will get a new Happy Feature option. In that section, you will find an option: Custom Column Width. Add the pixel number on the first column. Then in the second column, you can add the rest of the pixel number. Or if you want to add a percentage ration on the second column then you have to add the bellow equation:
= calc(100%-previously used pixel number)
Example: calc(100%-400px)
Learn more about pixel calculation from here.